Apparatus for mixing coreactive liquids which forms polyurethanes

ABSTRACT

A process and apparatus for intimately mixing two or more mutually coreactive liquids such as polyols and polyisocyanates comprising: A. passing the liquids, while in a substantially unmixed state, through a plurality of very small holes such as that provided by a screen, and immediately thereafter B. subjecting the liquids to a high shear. The present process and apparatus find particular utility in the production of high density, foamed polyurethane moldings.

United States Patent [191 Dunn [4 Nov. 27, 1973 [54] APPARATUS FORMIXING COREACTIVE 2,857,144 10/1958 Gurley 259/7 LIQUIDS WHICH FORMS3,051,455 8/1962 Magestcr 259/8 3,297,306 1/1967 Napier 259/8POLYURETHANES Inventor: Donald Dunn, Cincinnati, Ohio Assignee:Cincinnati Milacron Inc.,

Cincinnati, Ohio Filed: ,Jan. 27, 1972 Appl. No.: 221,175

Related US. Application Data Division of Ser. No. 878,081, Nov. 19,1969, Pat. No. 3,674,720.

US. Cl. 259/8 Int. Cl B01f 7/16 Field or Search 259/7, ,8, 23, 24,

References Cited UNITED STATES PATENTS 1/1969 Gurley 259/8 A process andapparatus for intimately mixing two or more mutually coreactive liquidssuch as polyols and polyisocyanates comprising:

Primary Examiner-Robert W. Jenkins AttorneyPlumley & Tyner ABSTRACT A.passing the liquids, while in a substantially unmixed state, through aplurality of very small holes such as that provided by a screen, and

immediately thereafter B. subjecting the liquids to a high shear.

' 4 Claims, 1 Drawing Figure APPARATUS FOR MIXING COREACTIVE LIQUIDSWHICH FORMS POLYURETHANES This is a division of application, Ser. No.878,081 filed Nov. 19, i969, now US. Pat. No. 3,674,720.

It is well-known in the art to intimately mix two mutually coreactiveliquids, at least one of which is very viscous, by subjecting. them tohigh shear in devices such as rotating mixers or centrifugal pumps.Examples of mutually coreactive liquids are polyols and polyisocyanatesemployed to produce rigid and flexible foamed polyurethane moldings.

Mixing equipment for the preparation of polyurethane foam can usually bedivided into two general categories. The first category includesequipment which employs high pressures (800 psi or more) to deliver theseparate reactive liquid components to a mixing chamber at the desiredweight ratio, where optionally under the influence of a stationaryhelical type member they are mixed and subsequently discharged fromthemixing chamber. The use of this high pressure equipment is limited bythe viscosity of the reactive liquid components which can be pumped bythe high pressure positive displacement fuel injection type pumps.Viscosities of l,000 cps or less are required for this high pressuretype equipment. Such Viscosities are typical of the reactive liquidcomponents used to obtain low density (2.0 lb/ft) polyurethane foam. Thesecond category includes equipment which uses low pressures (less than400 psi) to deliver the separate reactive liquid components to themixing chamber at the desired weight ratio where under the influence ofa high velocity, high 7 shear, rotating impeller they are mixed andsubsequently continuously discharged from the mixing chamber. This lowpressure type equipment is capable of pumping liquids having a muchhigher viscosity than those capable of being pumped in the high pressuretype equipment. Liquids having viscosities of several thousandcentipoises can be readily pumped in the low pressure type equipment.

Both low and high pressure type equipment often adequately mix lowviscosity reactive liquid components used for preparing low densitypolyurethane foam. Even in the preparation of higher density free blownfoam (e.g., 5 lbs/ft) adequate mixing of the relatively higher viscosityliquid components is often achieved with the low pressure typeequipment. It has been found, however, that the low pressure typeequipment often provides poor mixing of the high viscosity reactiveliquid components used to prepare high density rigid foam moldings asevidenced by uneven surface or internal color; non-uniform cell sizewithin the surface, skin, and core of the molding; an undesirably broadrange of cell size distribution; and an undesirably nonuniform cellseparation.

It is, therefore, an object of the present invention to provide a novelmixing apparatus substantially free of one or more of the disadvantagesof the prior art.

Another object is to provide a novel apparatus for intimately mixing twomutually coreactive liquids and especially viscous liquids;

A further object is to provide a novel apparatus for forming apolyobpolyisoeyanate mixture which can be used to produce foamedpolyurethane moldings having a uniform surface and internal color;aunlforin cell size within the surface. skin, andcore of the molding; anar new range of cell size distribution within the surface. skin, andcore; and uniform cell separation. Additional objects and advantageswill be apparent by the following detailed description of the presentinvention.

According to the present invention, it has been discovered that twomutually coreactive liquids such as polyols and polyisocyanates can beintimately mixed by passing the liquids through a plurality of verysmall holes and then subjecting the resultant mixture to a high shear.

The invention may be better understood by reference to the single FIGUREof the drawing wherein there is shown a partially cut-away isometricview of a preferred mixer of the present invention. The mixer com?prises a housing 10 having therein a cylindrical chamber 11. A rotor 12is rotatably mounted within the chamber 11 separated from the insidewall of the housing 10 by a distance, d, typically 0.010 inch to 0.030inch. The rotor 12 has a basket portion 13 and an impeller portion 14.The basket portion 13 of the rotor12 has vertically. disposed sides 15defining a cavity 16. The sides 15 are provided with a plurality ofslots 1-7. The slots 17 can have any shape but in the embodiment shownhave a length greater than three times the width (e.g., IAinch X 3/16inch). A screen 18 fits into the cavity 16 and rests on the bottomthereof and in contact with the inside surface of the sides 15. A driveshaft 21, driven by any suitable means not shown, is fixedly attached tothe rotor 12. The impeller portion 14 of the rotor 12 comprises aplurality of diamond shaped projections 19. The downstream or lowerportion of the housing 10 is in the shape of a funnel 20. Thepolyisocyanate is supplied to the inside of the screen 18 by conduit 22and the polyol is supplied by conduit 23. The impeller portion 14 of therotor 12 can have other well-known configurations such as those known inthe art as a standard spiral, banded spiral, or slotted spiral.

In operation the shaft 21 is rotated causing rotation of the rotor 12within the housing 10. The polyol optionally containing a blowing agentand the polyisocyanate are fed from reservoirs through conduits 22 and23 at the desired stoichiometric ratio and flow rate into the cavity 16.Due to the speed of rotation of the rotor ,12, the polyol and the.polyisocyanate are forced through the holes in the screen 18 under theinfluence of centrifugal force. Some mixing may occur in the cavity 16and the resulting partially mixed polyol and polyisocyanate then passthrough the screen 18 into a shear mixing zone formed by the inside wallof the chamber 11 and the outside wall of the basket portion 13. As thepolyolpolyisocyanate mixture comes into contact with the impellerportion 14 of the rotor 12, additional high shear mixing occurs with themixture finally being discharged from the housing 10 through the funnel20 prior to gelation. The mixture is then directed to molds not shownwhere the mixture cures to a rigid or flexible polyurethane molding.When the mixture contains a blowing agent, a polyurethane foam isproduced.

The holes through which the polyol and polyisocyanate pass can have amaximum cross-sectional dimension of 0.001 inch to 0.033 inch andpreferably from 0.0059 inch to 0.020 inch. Thus, when the holes areprovided in the form of drilled passages in the sides 15 of the basketportion 13 replacing the slots=1'7, these holes have diameters withinthe above-described limits. In the preferred embodiment of the inventionshown in the drawing wherein the holes are provided by the spacesbetween the wires of a woven screen, meshes of 20 to 400 and preferably32 to 200 mesh per inch are preferred. The sum of the areas of theindividual holes is at least great enough to permit the desiredthroughput of the mixture without creating an excessive pressure dropthrough the holes.

While the apparatus of the present invention intimately mixes liquids ofa wide variety of viscosities, it is especially useful for mixingliquids at least one of which has a viscosity of over 1,000 cps at themixing temperature. Such liquids are frequently employed in theproduction of high density (e.g., 5 lbs/ft) polyurethane foam moldings.

Organic polyisocyanates or mixtures of organic polyisocyanates, in theirliquid state, which are applicable in the practice of this inventioninclude, but are not limited to:

2, 4-Tolylene diisocyanate 2, 6-Tolyene diisocyanate '4,4-Diphenylmethane diisocyanate l, 6-Hexamethylene diisocyanate Mixturesof 2, 4- and 2, 6-Tolylene diisocyanates Xylylene diisocyanate Y 3,3'-Bitolylene-4, 4-diisocyanate Polymethylene polyphenyl isocyanateTrans vinylene diisocyanate 3, 3-Dimethoxy-4, 4'-diphenylenediisocyanate Hydrogenated 4, 4-diphenyl methane diisocyanate.

isocyanate-terminated reaction products, commonly known as prepolymers,obtained by reacting a stoichiometric excess of an organicpolyisocyanate or mixture of organic polyisocyanates with an organicpolyhydroxy compound or mixture of organic polyhydroxy compounds arealso applicable in the practice of this invention.

The organic polyhydroxy compounds or mixtures of organic polyhydroxycompounds, commonly used in the polyurethane art, which may be employedin the practice of this invention include, but are not limited lPoly(oxyalkylene derivatives of glycerine, sorbitol, a -methylglucoside, sucrose, trimethylol propane, pentaerythritol, starch or likealkyl, aryl, aryl-alkyl, cyclic or heterocyclic polyhydric alcohols.

2. Hydroxy terminated reaction products obtained by reactingpolycarboxylic acids with polyhydric alcohols (e.g., hydroxy terminatedreaction product of the reaction of ethylene glycol with adipic acid).

3. Poly(oxyalkylene)diols (e.g., poly(oxypropylene) diols,poly(oxyethylene )diols and poly(oxybutylene)diols).

4 4. Organic polyhydric alcohols (e.g., glycerine, "l, 6- hexane diol,ethylene glycol, neopentyl glycol and trimethlol propane.

5. Mixtures containing poly(oxyalkylene) derivatives of polyhydricalcohol and polyoxyalkylene diols or polyhydric alcohols (e.g.,poly(oxypropylated)a-methyl glucoside admixed with apoly(oxypropylene)diol).

6. Mixtures of polyoxyalkylated polyhydric alcohols.

7. Poly(oxyalkylene) derivatives of polyhydric alcohols admixed with thehydroxy terminated reaction products obtained by reacting polycarboxylicacids with a polyhydric alcohols (e.g., polyoxypropylated glycerineadmixed with the hydroxy terminated reaction product of the reaction ofethylene glycol with adipic acid).

Admixtures of organic polyisocyanates, isocyanateterminated prepolymersor organic polyhydroxy compounds with any or all of the following mayalso be employed in the practice of this invention:

blowing agents surfactants catalysts fillers pigments I fire retardantadditives U.V. stabilizers antioxidants.

The following non-limited examples wherein all parts and percentages areby weight further illustrate the present invention.

EXAMPLE .1

This control example illustrates the undesirable results obtained bycertain prior art procedures.

A polyisocyanate composition atabout 102F having a free isocyanatecontent of 25.3 percent by weight and a viscosity of 5,350 cps at 72Fprepared by reacting 1 1.7 parts by weight of Voranol P400 (apoly(oxypropylene) diol havingan average molecular weight of about 400and a hydroxyl number of about 270.3, obtainable from the Dow ChemicalCo.) with 88.3 parts by weight of Mondur MR (a polyisocyanate having afree isocyanate content of 31.56 percent by weight obtainable from theMobay Chemical Co.) and a polyol mixture at about 71F comprising 83.9parts by weight of Poly G-435DM (a propylene oxide-methyl glucosideadduct, propylene oxide-glycerine' adduct mixture having a hydroxylnumber of 439.6, obtainable from the Olin Mathieson Chemical Co.), 12.32parts by weight of monofluorotrichloromethane, 1.5 parts by weight ofDow Corning 193 surfactant (a silicone-glycol copolymer obtainable fromthe Dow Corning Corp.), 0.6 parts by weight of N, N, N N tetramethyl-l,3 butane diamine, and 1.68 parts by weight of difluorodichloromethaneat 53.5/46.5 polyisocyanate composition/polyol mixture ratio by weightwere injected into the mixing chamber of a Martin Sweets foam machine(Model VII pumping and metering unit, Model VMD-325 mixing head, andModel DD-2l mixing head drive) by means of constant displacement pumpsoperating at a combined output of 27.2 lbs/min. The liquid continuouslydischarged from the mixing chamber was passed into a closed aluminummold having a 166 in cavity, a mold temperature of about 142F or into a32 02. paper container. The approximately 900 grns. of material passedinto the mold, was permitted to foam and cure whereupon the resultantmolded foam article was removed. The liquid which passed into the 32 oz.paper container was allowed to foam and the resultant foam examined. TheMartin Sweets mixing chamber operating at an imeller speed of about4,900 rpm comprised (l) a rotating cylindrical member, known as theimpeller, having a plurality of diamond shaped projections equallydistributed over the external periphery and covering approximatelypercent of the length of the rotating cylindrical member and an uppersection covering approximately 30 percent of the length of the rotatingcylindrical member which is machined so as to form a cavity having aplurality of elongated openings (i.e., openings having a length manytimes the width) at the periphery, said openings having their long axisoriented at about 3045 to the long axis of the cylindrical member, and(2) a stationary tubular housingentirely covering the rotatingcylindrical member in a manner such that the stationary tubular housingand the rotating cylindrical member (impeller) are separated by a smalldistance, about 0.010 inches. At one end of the tubularhousing wasfastened a conically shaped member having a "V4 inch diameter opening atits apex. An essentially light brown cured foam molding was obtainedwhich exhibited non-uniform surface and internal color (i.e., thesurface and interior portions of the foam molding both containednumerous dark brown isocyanate rich-looking regions of random size andshape distributed in a random manner). The molding exhibited anon-uniform cell structure at the surface and interior, with respect tocell size and distribution of cell sizes. The light brown regions of themolding contained a relatively narrow distribution of relatively 7 smallcells while the dark brown regions exhibited a rather wide distributionof cell sizes (i.e., some cells were quite large, being larger than thecells inthe light brown regions and some cells were quite small, beingmuch smaller than the cells inthe light brown regions).

The free blown foam also exhibited considerable variation in color andcell structure. Regions of significantly darker color wererandomlydistributed throughout the body of the foam. These darker coloredisocyanate rich-looking regions contained a wide distribution of cellsizes, some cells being rather large while other cells appearedrelatively small. On the other hand, the lighter colored regionsexhibited a relatively narrow distribution of cell sizes.

EXAMPLE 2 of the Martin Sweets foam machine described in Examplel,'which was modified by placing a 32 mesh per inch wire screen at theinternal periphery of the cavity of the upper section of the impeller,at a polyisocyanate composition/polyol mixture ratio of 535/465 byweight using two constant displacement pumps operating at a combinedoutput of 27.2 lbs/min. The 32 mesh wire screen covered the elongatedopenings in the cavity section of the impeller of Example 1. An impellerspeed of 4,900 rpm was used and the liquid being continuously dischargedfrom the mixing chamber was passed into the closed aluminum mold ofExample 1 at a mold temperature of 140F or into a 32 oz. papercontainer. The approximately 900 grams of materials in the aluminum moldwas permitted to foam and resultant cured molded foam article wasremoved and examined. The material in the 32 02. paper container waspermitted to free blow and set whereupon it was examined.

The molded foam article exhibited an improved uniformity of color on thesurface as compared to the surface of the foam molding of Example 1.Cell structure uniformity on the surface of the foam molding of Example2 was greater than the cell structure uniformity on the surface of thefoam molding of Example 1 (i.e., the distribution of cell sizes on thesurface of the foam molding of Example 2 was narrower than thedistribution of cell sizes on the surface of the foam molding of Example1 The interior of the molding of Example 2 exhibited a relativelyuniform color and cell structure in contrast to the non-uniform colorand cell structure of the interior of the foam molding of Example 1.Relative to the cell size distribution in the interior of the foammolding of Example 1 the distribution of cell sizes in the interior ofthe foam molding of Example 2 appears to be narrow. The free blown foamof Example 2 exhibited a uniform color throughout as compared to thenon-uniform color of the free blown foam of Example 1.

EXAMPLE 3 A polyisocyanate composition at about 97F having a freeisocyanate content of 25.4 percent by weight and a viscosity of 4925 cpsat F prepared by reacting Voranol P400 (a poly(oxypropylene) diol havingan average molecular weight of about 400 and a hydroxyl number of about270.3, obtainable from the Dow Chemical Co.) with Mondur MR (apolyisocyanate having a free isocyanate content of 31.23 percent byweight obtainable from the MobayChemical Co.) and i a polyol mixture atabout 68F comprising 83.9 parts by r weight of Poly G-435DM (a propyleneoxide methyl glucoside adduct, propylene oxide-glycerine adduct mixturehaving a hydroxyl number of 435.3, obtainable from the Olin MathiesonChemical Co.), 12.32 parts by weight of monofluorotrichloromethane, 1.50parts by weight of Dow Corning 193 surfactant (a siliconeglycolcopolymer obtainable from the Dow Corning Corp.), 1.68 parts by weightof dlifluorodichloromethane, and 0.6 parts by weightof N, N, N, Ntetramethyl-l,3-butane diamine at 53.l/46;9 polyisocyanatecomposition/polyol mixture ratio by weight were injected into the mixingchamber of a Martin Sweets foam machine (Model VII pumping and meteringunit, size 4 MH4FPG mixing head), said mixing chamber being of the typedescribed in Example 1, operating at an impeller speed of 5,300 rpm,said impeller being of the type described in Example 1 and to be knownas the reverse spiral impeller, by means of constant displacement pumpsoperating at a combined output of 20.4 lbs/min. The liquid streamdischarged from the mixing chamber was passed into a 166 in closedaluminum mold at about 'amold temperature of F or into a 32 02. papercup. The approximately 900 grams of material passed into the aluminummold was allowed to foam and cure whereupon the resultant article wasremoved. The material which passed into the paper cup was permitted tofoam freely and the resultant foam examined. The article removed fromthe mold exhibited a non-uniform surface color which comprised areas ofrelatively light tan color and randomly distributed areas, of randomsize, having a darker (i.e., brown) color. The relatively light tanareas exhibited a uniform cell structure composed of relatively smalldiameter cells (i.e., the distribution of cell sizes was narrow and theaverage cell size being relatively small) while the darker coloredisocyanate rich-looking areas exhibited a non-uniform cell structurehaving an average cell diameter which was relatively large (i.e., thedistribution of cell sizes was wide and the average cell diameterrelatively large). Non-uniform color and cell structure was obtained inthe core foam of the molding. The core foam of the molding containedregions of very light color and randomly distributed darker coloredisocyanate rich-looking regions. Cell structure was uniform in the lightcolored. regions and the average cell diameter relatively small, whilein the darker colored regions the cell structure was non-uniform and theaverage cell-diameter relatively large (i.e., the distribution of cellsizes was wide and the average cell diameter relatively large).Non-uniform color and cell structure was obtained in the free blownfoam. Relatively dark colored isocyanate rich-looking regions having anon-uniform cell structure and a relatively large average cell diameterwere distributed randomly throughout the bulk of the free blown foam.The very light colored regions of the free blown foam exhibited auniform cell structure having a relatively small average cell diameter.

EXAMPLE 4 A polyisocyanate composition at about 99F having a freeisocyanate content of 25.64 percent by weight and a viscosity of 6,550cps at 70F prepared by reacting Voranol P400 (a poly(oxypropylene) diolhaving. an average molecular weight of about 400 and a hydroxyl numberof about 270.3, obtainable from the Dow Chemical Co.) with Mondur MR (apolyisocyanate having a free isocyanate content of about 31.28 percent,obtainable from, the Mobay Chemical Co.) and the polyol mixture ofExample 3 at about 68F at a 52.7/47.3 polyisocyanate composition/polyolmixture ratio by weight were injected into the mixing chamber of Example3 of the Martin Sweets foam machine of Example 3, modified to include a60 X 60 mesh (60 openings per inch) wire screen at the entire internalperiphery of the impeller basket of the impeller of Example 3, by meansof constant displacement pumps operating at a combined output of 20.6lbs/min. The impeller of the mixing chamber was operated at 5,300 rpm.Approximately 900 grams of the liquid stream being discharged from themixing chamber was directed into a 166 in closed aluminum mold at a moldtemperature of 132F. The liquid in the mold was permitted to foam andthe resulting foam article cured in the mold. A foam molding wasobtained which exhibited a slight non-uniformity of surface color onlyat one corner. The remaining surface comprising 95 percent of the entiremolding, exhibited uniform color and uniform cell structure as opposedto the general non-uniform color and cell structure obtained on thesurface of the molding of Example 3. The core foam of the resultingmolding exhibited a uniform very light color and a uniform mutuallycoreactive liquids comprising a. a stationary cylindrical housing havinga cylindrical chamber therein and being open at both ends; b. acylindrical rotor rotatably mounted within said chamber in closeproximity to the wall of said chamber and having 1. a cylindrical hollowportion defined by a wall normal to the diameter of said hollow portionwhich contains a plurality of holes each having a maximumcross-sectional dimension, excluding their longitudinal dimension, of0.001 to 0.033 inch; and 2. a portion for imparting high shear to theliquids coming between said rotor and the wall of the chamber; c. ameans for separately and simultaneously passing a plurality of liquidsinto the hollow portion of the v rotor; and

d. a means for causing rotation of the rotor.

2. The apparatus of claim 1 wherein said rotor is separated from-theinside surface of said cylindrical chamber by a distance of from 0.01 to0.20 inches.

3. An apparatus for intimately mixing at least two mutually coreactiveliquids comprising a. a stationary cylindrical housing having acylindrical chamber therein and being open at both ends,

b. a cylindrical rotor rotatably mounted within said chamber in closeproximity to the wall of said chamber and having (1) a cylindricalhollow portion defined by a wall normal to the diameter of said hollowportionwhich contains a plurality of passageways extending from theinside surface to the outside surface .of said wall and (2) a portionfor imparting high shear to the liquids coming between said rotor andthe wall of the chamber,

c. a cylindrical screen of 20 to 400 mesh per inch disposed within saidhollow portion ofsaid rotor, in contact with the wall defining thehollow portion of said rotor,

d. a means of separately and simultaneously passing a plurality ofliquids intofthe hollow portion of the rotor,

e. a means for causing rotation of the rotor.

4. The apparatus of claim 3 wherein said rotor is separated from theinside surface of said cylindrical chamber by a distance of from 0.01 to0.20 inches.

"UNITED STATES PATENT OFFICE V 1 CERTIFICATE OF CORRECTION Patent No. 3774 887 Dated November 27 1973 Inventor(s) Donald Dunn It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Colu'mn 8 Claims 2 and 4 line 3 ---0.01 to -.03 inches- Signed andsealed this 10th day of September} 1 (sEAL) Attest:

McCOY M. GIBSON; JR. r C. MARSHALLDANN Attesting Officer Commissioner ofPatents FORM PO-1050 (10-69) I u'scoMM-oc scan-Poo fi 0,5. GOVERNMENTPR'NTIHG OFFICE I96! 0-36-331

2. The apparatus of claim 1 wherein said rotor is separated from theinside surface of said cylindrical chamber by a distance of from 0.01 to0.20 inches.
 2. a portion for imparting high shear to the liquids comingbetween said rotor and the wall of the chamber; c. a means forseparately and simultaneously passing a plurality of liquids into thehollow portion of the rotor; and d. a means for causing rotation of therotor.
 3. An apparatus for intimately mixing at least two mutuallycoreactive liquids comprising a. a stationary cylindrical housing havinga cylindrical chamber therein and being open at both ends, b. acylindrical rotor rotatably mounted within said chamber in closeproximity to the wall of said chamber and having (1) a cylindricalhollow portion defined by a wall normal to the diameter of said hollowportion which contains a plurality of passageways extending from theinside surface to the outside surface of said wall and (2) a portion forimparting high shear to the liquids coming between said rotor and thewall of the chamber, c. a cylindrical screen of 20 to 400 mesh per inchdisposed within said hollow portion of said rotor, in contact with thewall defining the hollow portion of said rotor, d. a means of separatelyand simultaneously passing a plurality of liquids into the hollowportion of the rotor, e. a means for causing rotation of the rotor. 4.The apparatus of claim 3 wherein said rotor is separated from the insidesurface of said cylindrical chamber by a distance of from 0.01 to 0.20inches.